The present invention relates to methods and apparatuses for effecting adhesion, and particularly to methods and apparatuses for producing multi-laminate microfabricated, including microfluidic, devices.
Recently, techniques first developed for the manufacture of microelectronic devices have been adapted to the manufacture of a wide variety of microfluidic devices for chemical analysis and synthesis.
For example, Wilding et al., U.S. Pat. No. 5,587,128, disclose devices particularly adapted for nucleic acid amplification, constructed by fabricating flow channels and one or more reaction chambers into the surface of a planar substrate; at least one of these engineered features has a cross-sectional diameter between 0.1 xcexcm and 1,000 xcexcm.
Zanzucchi et al., U.S. Pat. No. 5,593,838, disclose a microlaboratory disc variously adapted for performing nucleic acid assays or immunoassays, or for synthesizing peptides, oligonucleotides, or other combinatorially-constructed small molecules. The disc comprises a plurality of modular assay units, each comprising one or more arrays of sample wells 200-750 microns deep, interconnected by one or more channels at equivalent scale. Etching from both sides of the planar substrate permits the fabrication of a more complex network of overlapping capillary channels of similar dimensions, Zanzucchi et al., U.S. Pat. No. 5,681,484.
Heller et al., U.S. Pat. No. 5,605,662, describe microfluidic devices containing matrices of micron-sized locations, each of which is underlaid with a distinct and separately addressable microelectrode. The device is adapted to drive diagnostic and synthetic reactions, including nucleic acid hybridization and immunoassays.
Parce, U.S. Pat. No. 5,699,157, describes a microfluidic system for electrophoretic analysis of materials migrating in a microchannel fabricated in a planar substrate. The microchannels, fabricated by standard photolithographic or micromachining methods, such as laser drilling, range in diameter from about 0.1 xcexcm to 100 xcexcm.
WO 96/04547 (Lockheed Martin Energy Systems) describes a microchip laboratory system with micron-sized channels fabricated using standard photolithographic procedures and chemical wet etching, for use in capillary electrophoresis, DNA sequencing, gradient elution liquid chromatography, flow injection analysis, and chemical reaction and synthesis.
Chow et al., U.S. Pat. No. 5,800,690 describe microfluidic systems fabricated with a plurality of electrodes at nodes of a two-dimensional network of interconnecting capillary channels etched into a planar substrate; the electrodes create electric fields that move fluid-entrained materials electrokinetically through the channels.
Although the microfabrication techniques designed for semiconductor manufacture have proven useful in the precise fabrication of micron and sub-micron channels, wells, and other etched features in planar substrates, these techniques have not proven sufficient for completing the manufacture of many of these microfluidic systems. In particular, the techniques of photolithography, micromachining, vapor deposition and the like have proven ill-suited to the manufacture of microscopic features that are fluidly sealed.
Thus, to convert channels and wells into fluidly sealed capillaries and chambers, respectively, Wilding, U.S. Pat. No. 5,587,128, directs, without further explanation, that a cover be adhered or clamped to the planar substrate into which the engineered features have been etched. Chow et al., U.S. Pat. No. 5,800,690, and Parce, U.S. Pat. No. 5,699,157, analogously teach that a planar cover element be laid over the channeled substrate, and suggest generally that the planar cover element be attached to the substrate by thermal bonding, application of adhesives, or by natural adhesion between the two components.
But each of these proposed approachesxe2x80x94thermal bonding, application of adhesives, or natural (direct) adhesionxe2x80x94presents difficulties.
Although thermal bonding may be effective, sealing must be achieved at a temperature sufficiently low as to avoid distortion or destruction of the underlying substrate or substrate-embedded features. When the substrate and cover are silicon or glass, Zanzucchi et al., U.S. Pat. No. 5,593,838, teach that localized application of electric fields permits the meltable attachment of the cover element at about 700xc2x0 C., well below the flow temperature of silicon (about 1400xc2x0 C.) or of Corning 7059 glass (about 844xc2x0 C.) WO 96/04547 (Lockheed Martin Energy Systems) teaches that a cover plate may be bonded directly to a glass substrate after treatment in dilute NH4OH/H2O2, followed by annealing at 500xc2x0 C., well below the flow temperature of silicon-based substrates.
Recently, however, microfluidic laboratories have been proposed that may be constructed using plastic substrates. See, e.g., WO 97/21090 and WO 98/53311 (Gamera Bioscience); WO 96/09548 (Molecular Drives); EP A 0392475, EP A 0417305, and EP A 0504432 (Idemitsu). International applications published as WO 98/01533, WO 98/37238, and WO 98/38510, describe aspects of microfluidic platforms that are particularly adapted for detection by optical disk readers, such as CD and DVD readers; these assay disks are, accordingly, typically constructed using techniques and materials first developed in the optical disk arts. The plastics so used may melt or deform at temperatures far below those tolerated by silicon and glass.
There thus exists a need in the art for adhesion methods that permit lamination at temperatures sufficiently low as to prevent deformation or melting of plastic substrates. Furthermore, adhesion must be achieved at temperatures that prevent denaturation of biological macromolecules, such as antibodies, that may be disposed in and upon such substrates.
WO 98/45693 (Aclara Biosciences) discloses, inter alia, a thermal bonding method for fabricating enclosed microchannel structures in polymeric, particularly plastic, substrates. After apposing the planar surfaces of the two adherends, the temperature is maintained above the glass transition temperature of the polymer for a time sufficient to allow the polymer molecules to interpenetrate, and thus to bond, the two surfaces. Although the temperatures used are lower than those used in thermal bonding of semiconductors, the approach requires that the apposing planar surfaces of the base plate and cover be made of similar polymeric materials, and the temperatures may still be sufficient to cause deterioration of the optical properties at the interface. There thus still exists a need for a method of low temperature bonding that permits the adhesion of laminae of dissimilar polymeric materials without substantial optical distortion at the bonding interface.
Lamination using adhesives presents its own problems, principal among which is the potential for extrusion of adhesive from the bonding interface into the microfabricated channels and chambers formed between the laminae.
Beattie, U.S. Pat. No. 5,843,767, teaches that such extrusion may be prevented by the laser ablation of adhesive from selected areas of one of the adherends prior to adhesion. The prior ablation adds an additional fabrication step to the process, however, and serves to reduce the bonded surface area. WO 98/45693 (Aclara Biosciences) proposes to prevent extrusion by applying adhesive in a film no more than 2 xcexcm thick, and in fluid curable embodiments further to control extrusion by rendering the adhesive nonflowable by partial curing before apposition of adherends. Each of these latter approaches requires careful attention to process.
There thus exists a need in the art for lamination methods that more readily prevent extrusion of adhesive from between adherent laminae and that may be used in a rapid process.
Bonding of laminae using adhesives presents other problems as well, many of which are exacerbated at microfabrication scale.
For example, physical application of such small volumes of adhesive may prove difficult, particularly within the temporal limits imposed by the induction time and curing time of a fluid-phase adhesive. Furthermore, as the thickness of the adhesive layer decreases, the probability increases that the adhesive layer will include tiny pinhole areas lacking adhesive coating. These uncoated areas may be subject to chemical attack, which can weaken the bonding interface. There thus exists a need in the art for adhesives that are more readily and uniformly applied to surfaces of small scale adherends, and that lack the temporal restraintsxe2x80x94that is, limited potlifexe2x80x94imposed by induction and curing of standard fluid-phase adhesives.
Direct adhesion of planar surfaces, which has been described particularly in the bonding of semiconductor wafer surfaces, presents yet other problems. Direct wafer bonding is effectuated by oxidizing the surfaces of mirror polished silicon wafers, then fusing the oxidized (glass) surfaces at high temperature (400xc2x0 C.-1,200xc2x0 C.) with application of external uniaxial pressure to create covalent bonds between the wafers. See Kish et al., U.S. Pat. No. 5,783,477. This process relies, however, upon the intrinsic behavior of the silicon surfaces, and is therefore limited in the types of materials that may be bonded and in the bond strengths obtainable.
Linn et al., U.S. Pat. No. 5,849,627, describe a modification of the wafer bonding approach in which further application of an aqueous oxidizing solution between the wafers during the annealing step adds a further redox reaction to the standard reaction of silicon dioxide surfaces. The addition of the further reactant permits slight reduction in the annealing temperature and allows variation in the bond chemistry and strength between the wafers. Nonetheless, the chemistries described are adapted particularly to bonding silicon surfaces, and the temperatures required for annealing remain high (800xc2x0 C.-1000xc2x0 C.).
There thus exists a need in the art for adhesion methods that allow close, preferably monomolecular, bonding of surfaces that are not necessarily silicon-based, and that may comprise dissimilar polymeric substrates. There further exists a need for direct adhesion methods that permit annealing at temperatures below the deformation or melting temperatures of standard plastics.
Apparatuses for effecting continuous production of laminated bodies have been described. Seifried et al., U.S. Pat. No. 5,228,944; Schmidt et al., U.S. Pat. No. 5,698,299. Schmidt et al. particularly describe continuous manufacture of microfluidic devices by registrable superimposition of patterned microfabricated laminae. In each of these approaches, however, laminae are bonded by standard thermal adhesion or fluid adhesive methods, importing into the continuous manufacturing processes the shortcomings concomitant to such adhesive methods. There thus exists a need for methods and apparatuses for effecting continuous production of laminated bodies using low temperature direct adhesion of laminae.
The present invention solves these and other problems in the art by presenting low temperature adhesion methods that bond surfaces of various composition monomolecularly at low temperature. The invention is based, in part, upon the novel recognition that direct adhesion may be effected between two macroscopic adherends by separately rendering each bonding surface competent to contribute a reactant to a chemical bonding reaction; when a sufficient density of reactive groups have been disposed upon the bonding surfaces, the formation of a large number of chemical bonds between the two surfaces after contact suffices directly to affix the adherends to one another. If one or both surfaces, by virtue of their composition, inherently displays a sufficient density of an appropriate reactant, a separate step need not be performed to render the surface competent for adhesion.
Thus, in a first aspect, the invention provides a method of attaching a first bonding surface to a second bonding surface, comprising the step of contacting the first bonding surface to the second bonding surface, wherein a first reactant for a chemical bonding reaction is plurally present on the first bonding surface, a second reactant for the chemical bonding reaction is plurally present on the second bonding surface, and the surfaces are contacted for a time and under conditions sufficient to permit the chemical reaction to bond a sufficient number of first reactants to second reactants to attach the first bonding surface to said second bonding surface.
The method may further comprise the antecedent step of disposing upon the first bonding surface a plurality of the first reactant, and may also comprise the additional step, prior to contacting the bonding surfaces, of disposing upon the second bonding surface a plurality of the second reactant. In preferred embodiments of these latter methods, the derivatization step includes exposure of at least one of the bonding surface to a gas plasma, such as ammonia plasma, oxygen plasma, and halogen plasmas; exposure to anhydrous ammonia plasma particularly may be used to aminate the bonding surface for reaction with epoxide groups presented by the second bonding surface.
The chemical reaction that bonds the adherend surfaces may form covalent bonds, hydrogen bonds, ionic bonds, or dative bonds. Covalent bonds are preferred for strong adherence. Dative, or coordinate bonds, also prove useful, particularly when such bond includes coordination of a metal, particularly coordination of gold by free sulfhydryl group.
In a second aspect, the invention provides a method of attaching a first bonding surface to a second bonding surface, comprising the step of contacting the first bonding surface to the second bonding surface in the presence of a linker molecule, wherein a first reactant for a first chemical bonding reaction is plurally present on the first bonding surface, a first reactant for a second chemical bonding reaction is plurally present on the second bonding surface, wherein the linker includes a second reactant for the first chemical bonding reaction and a second reactant for the second chemical bonding reaction, and the surfaces and linker are contacted for a time and under conditions sufficient to permit the first and second chemical reactions to bond the linker concurrently to both first and second bonding surfaces in numbers sufficient to attach the first bonding surface to the second bonding surface.
This second method may further comprise the antecedent step of disposing upon the first bonding surface a plurality of the first chemical reaction first reactant, and optionally a further step, before the contacting step, of disposing upon the second bonding surface a plurality of the second chemical reaction first reactant. In preferred embodiments of these latter methods, the derivatization step includes exposure of at least one of the bonding surface to a gas plasma, such as ammonia plasma, oxygen plasma, and halogen plasmas; exposure to anhydrous ammonia plasma particularly may be used to aminate the bonding surface for reaction with epoxide groups presented by the linker molecule.
By analogy to the methods of the first aspect of this invention, the chemical reaction that bonds the adherend surfaces may form covalent bonds, hydrogen bonds, ionic bonds, or dative bonds. Covalent bonds are preferred for strong adherence. Dative, or coordinate bonds, also prove useful, particularly when such bond includes coordination of a metal, particularly coordination of gold by free sulfhydryl group.
Although uniform application of the linker to one of the two bonding surfaces will, after complete reaction, effectively recreate the adhesive geometry presented by the methods of the first aspect of the invention in which the bonding surfaces are competent to bind directly to one another, nonuniform application of the linker to an adherend surface creates one or more discrete spots on that surface that is capable of contributing to a bond. The creation of spatially-directed bonding locations permits xe2x80x9cspot-weldingxe2x80x9d of adherends, which may provide certain structural benefits to the microfabricated object by providing nonbonded areas to relieve stress; additionally, the creation of spatially-directed bonding locations permits the directed attachment of microfabricated components to the surface of the adherend.
The methods of the present invention permit the low temperature adhesion of surfaces of various compositions. Thus, in particular embodiments, at least one of said bonding surfaces is of an adherend consisting essentially of plastic. In a preferred embodiment, the plastic is polycarbonate or polystyrene. In other embodiments, at least one of said bonding surfaces is of an adherend consisting essentially of metal, preferably gold. The methods thus readily permit the application of metal foils to formed plastics, which proves useful in the rapid and continuous manufacture of optical disks and microfabricated analytical devices readable by optical disk readers.
The methods are not limited to planar substrates. Thus, the bonding surface of at least one of the adherends may include features that are nonplanar with the bonding interface; such nonplanarities may include channels, wells, or the like etched or micromachined into the surface, permitting the construction of microfluidic devices. Thus, in certain embodiments of the adhesion methods of the present invention, at least one of the bonding surfaces includes nonplanarities with the bonding interface, such as features etched or micromachined from the surface into the substrate of the adherend. In preferred embodiments, the attachment of the second adherend fluidly encloses the nonplanar feature. Alternatively or additionally, the nonplanarities may digitally encode information; in preferred embodiments, that digitally encoded information, for example in the form of pits or grooves, is readable by an optical disk reader. In yet other embodiments, at least one of said bonding surfaces has analyte-specific signal elements disposed thereon, preferably analyte-specific signal elements readable by an optical disk reader.
The methods for adhering a first bonding surface to a second bonding surface may readily be used in the manufacture of multilaminate structures.
Thus, in another aspect, the invention provides a method for constructing a multilaminate structure, the method comprising at least one iteration of the step of: attaching a first adherend to a second adherend, the attached adherends serving as first adherend in any subsequent iteration of the step, wherein the attaching step is performed by contacting a bonding surface of the first adherend to a bonding surface of the second adherend, wherein a first reactant for a chemical bonding reaction is plurally present on the first adherend bonding surface, a second reactant for the chemical bonding reaction is plurally present on the second adherend bonding surface, and the surfaces are contacted for a time and under conditions sufficient to permit the chemical reaction to bond a sufficient number of first reactants to second reactants to attach the first adherend bonding surface to the second adherend bonding surface.
The invention provides a further method for constructing a multilaminate structure, the method comprising at least one iteration of the step of: attaching a first adherend to a second adherend, the attached adherends serving as first adherend in any subsequent iteration of the step, wherein the attaching step is performed by contacting a bonding surface of the first adherend to a bonding surface of the second adherend in the presence of a linker molecule, wherein a first reactant for a first chemical bonding reaction is plurally present on the first adherend bonding surface, wherein a first reactant for a second chemical bonding reaction is plurally present on the second adherend bonding surface, wherein the linker includes a second reactant for the first chemical bonding reaction and a second reactant for the second chemical bonding reaction, and the surfaces and linker are contacted for a time and under conditions sufficient to permit the first and second chemical reactions to bond the linker concurrently to the first adherend surface and the second adherend surface in numbers sufficient to attach the first adherend to the second adherend.
The invention provides, in another aspect, a multilaminate structure produced by at least one iteration of either of these processes.
The methods of the present invention are particularly suitable and present significant advantages for use in rapid continuous laminating processes in which adherends, usually formed as flexible sheets or films, are contacted progressively in a continuous fashion.
Thus, in yet another aspect, the invention provides a method of manufacturing a multilaminate structure, the method comprising at least one iteration of the step of: attaching a first adherend to a second adherend, the attached adherends serving as first adherend in any subsequent iteration of the step, wherein the attaching step is performed by progressively contacting a bonding surface of the first adherend to a bonding surface of the second adherend, wherein a first reactant for a chemical bonding reaction is plurally present on the first adherend bonding surface, a second reactant for the chemical bonding reaction is plurally present on the second adherend bonding surface, and the surfaces are contacted for a time and under conditions sufficient to permit the chemical reaction to bond a sufficient number of first reactants to second reactants to attach the adherends.
The invention further provides a second method for manufacturing a multilaminate structure, the method comprising at least one iteration of the step of: attaching a first adherend to a second adherend, the attached adherends serving as first adherend in any subsequent iteration of the step, wherein the attaching step is performed by progressively contacting a bonding surface of the first adherend to a bonding surface of the second adherend in the presence of a linker molecule, wherein a first reactant for a first chemical bonding reaction is plurally present on the first adherend bonding surface, wherein a first reactant for a second chemical bonding reaction is plurally present on the second adherend bonding surface, wherein the linker includes a second reactant for the first chemical bonding reaction and a second reactant for the second chemical bonding reaction, and the surfaces and linker are contacted for a time and under conditions sufficient to permit the first and second chemical reactions to bond the linker concurrently to the first adherend surface and second adherend surface in numbers sufficient to attach the adherends.